1. Field of the Invention
The present invention relates to a touch panel and a display device with a built-in touch panel, and more particularly, to a technology effectively applicable to a touch panel including scanning electrodes and detecting electrodes, which are formed on different surfaces.
2. Description of the Related Art
A display device which includes a device for inputting information by a touch operation (contact press operation; hereinafter, simply referred to as touch) onto a display screen with the use of a user's finger or a pen (hereinafter, the device is referred to also as touch sensor or touch panel) is used for mobile electronic devices such as a PDA and a mobile terminal, various home electric appliances, an automated teller machine, and other such devices. As the touch panel, there are known a resistive type touch panel that detects a change in resistance at a touched portion, a capacitance type touch panel that detects a change in capacitance, and an optical sensor type touch panel that detects a change in light intensity (US 2007/0262966).
In the capacitance type touch panel, vertical detection electrodes (X electrodes) and horizontal detection electrodes (Y electrodes) are vertically and horizontally arranged in matrix in two dimensions, and the capacitance of each electrode is detected by an input processing portion. When a conductor such as a finger contacts with the surface of the touch panel, the capacitance of each electrode increases. The input processing portion detects the increase in capacitance, and calculates input coordinates based on a signal of the capacitance change detected by each electrode.
FIGS. 1A and 1B are diagrams illustrating a conventional display device with a touch panel.
FIG. 1A is a block diagram illustrating a schematic configuration of the conventional display device with a touch panel, and FIG. 1B is a diagram illustrating a structure of the conventional display device with a touch panel.
As illustrated in FIG. 1B, a capacitance type touch panel 106 is adhered onto a display device (in this case, liquid crystal display panel) 101 with an adhesive 110. As described later, the touch panel 106 includes X electrodes and Y electrodes for capacitance detection.
The touch panel 106 is arranged in front of the display panel 101. Therefore, in order to enable an image displayed on the display panel 101 to be viewed by a user, the displayed image is required to transmit the touch panel 106. Therefore, the touch panel 106 is desired to have a high light transmittance.
The X electrodes and the Y electrodes of the touch panel 106 are connected to a touch panel control portion 108 through wiring 107.
The touch panel control portion 108 sets the Y electrodes as scanning electrodes and sequentially applies a drive voltage thereto, and sets the X electrodes as detecting electrodes to measure interelectrode capacitances at respective electrode intersections. The touch panel control portion 108 calculates and determines input coordinates from capacitance detection signals which vary depending on capacitance values of the respective electrode intersections.
The touch panel control portion 108 uses an I/F signal 109 to transfer the input coordinates to a system control portion 105.
When the input coordinates are transferred from the touch panel 106 by a touch operation, the system control portion 105 generates a display image in accordance with the touch operation, and transfers the generated display image to a display control circuit 103 as a display control signal 104.
The display control circuit 103 generates a display signal 102 in accordance with the display image transferred by the display control signal 104, to thereby display an image on the display panel 101.
Note that, any display panel can be used as long as the display panel can be used with the touch panel 106, and the display panel is not limited to a liquid crystal display panel. Alternatively, it is possible to use a display panel which uses an organic light emitting diode element or a surface-conduction electron emitter, or an organic EL display panel.
When a liquid crystal display panel is used as the display panel 101, the display panel 101 includes a backlight unit (not shown) arranged below a surface of the liquid crystal display panel on a side opposite to the viewer side. The liquid crystal display panel used in this case is, for example, an IPS type, TN type, or VA type liquid crystal display panel.
As is well known, the liquid crystal display panel is formed by adhering two substrates arranged opposed to each other, and polarizing plates are provided on outer sides of the two substrates, respectively.
FIGS. 2A and 2B are diagrams illustrating the touch panel 106.
FIG. 2A is a diagram illustrating an electrode pattern of the touch panel 106, and FIG. 2B is a sectional view illustrating a sectional structure taken along the cut-line IIB-IIB of FIG. 2A.
As illustrated in FIG. 2A, the touch panel 106 includes X electrodes 201 and Y electrodes 202 for capacitance detection. In this case, for example, five X electrodes 201 and six Y electrodes 202 are illustrated, but the number of the electrodes is not limited thereto.
FIG. 2B illustrates a touch panel substrate 204 formed of a glass substrate, a PET film, or the like. In the touch panel 106, the X electrodes 201 and the Y electrodes 202 are formed on the touch panel substrate 204, and a protective film 203 is formed on the X electrodes 201 and the Y electrodes 202. Further, in FIG. 2B, a shielding electrode 205 is formed on a surface of the touch panel substrate 204 on the display panel side.
FIGS. 3A and 3B are diagrams illustrating a conventional display device with a built-in touch panel.
FIG. 3A is a block diagram illustrating a schematic configuration of the conventional display device with a built-in touch panel, and FIG. 3B is a diagram illustrating a sectional structure of the conventional display device with a built-in touch panel.
As illustrated in FIG. 3B, a capacitance type touch panel 301 is formed inside a display device (in this case, liquid crystal display panel) 101. Other configurations are the same as those of FIG. 1A, and hence repetition of detailed description thereof is omitted. FIGS. 4A and 4B are diagrams illustrating the touch panel 301. FIG. 4A is a diagram illustrating an electrode pattern of the touch panel 301, and FIG. 4B is a sectional view illustrating a sectional structure taken along the cut-line IVB-IVB of FIG. 4A.
As illustrated in FIG. 4A, the touch panel 301 includes X electrodes 201 and Y electrodes 202 for capacitance detection. In this case, for example, five X electrodes 201 and six Y electrodes 202 are illustrated, but the number of the electrodes is not limited thereto.
FIG. 4B illustrates a first substrate 211, a second substrate 212, a lower polarizing plate 213, an upper polarizing plate 214, a liquid crystal layer 215, and a sealing member 216. As illustrated in FIG. 4B, the X electrodes 201 and the Y electrodes 202 are formed at different parts of the structural members of the liquid crystal display panel.
Note that, the first substrate 211 and the second substrate 212 are desired to have a high light transmittance.
Further, generally, in an IPS type liquid crystal display panel, on a surface of the first substrate 211 on the liquid crystal layer side, there are formed, in the order from the first substrate 211 toward the liquid crystal layer 215, scanning lines (also referred to as gate lines), an interlayer insulating film, video lines (also referred to as source lines or drain lines), thin film transistors (TFTs), pixel electrodes, an interlayer insulating film, counter electrodes (also referred to as common electrodes), and an alignment film. In FIG. 4B, however, illustration of those members is omitted.
Further, on a surface of the second substrate 212 on the liquid crystal layer side, there are formed, in the order from the second substrate 212 toward the liquid crystal layer 215, alight shielding film, color filters of red, green, and blue, a planarization film, and an alignment film. In FIG. 4B, however, illustration of those members is omitted.
In the structure of FIG. 4B, a back electrode formed on a surface of the second substrate on a side opposite to the liquid crystal layer doubles as the X electrode 201, and the counter electrode doubles as the Y electrode 202.
FIGS. 5A to 5C are diagrams illustrating a conventional detection method for the touch panel 106. FIG. 5A is a diagram illustrating a state in which a touch operation is not performed, FIG. 5B is a diagram illustrating a state in which a finger 502 has approached the touch panel 106, and FIG. 5C is a graph showing variations of detected signals.
One of the X electrode 201 and the Y electrode 202 (in this case, the Y electrode 202) is connected to a voltage source 504 so that a pulse is input thereto from the voltage source 504. A transient current associated with the pulse input from the voltage source 504 is detected by a detection circuit (505, 506) via the other electrode at which capacitive coupling occurs (in this case, the X electrode 201). As illustrated in FIG. 5A, the capacitive coupling forms lines 501 of electric force between the X electrode and the Y electrode.
As illustrated in FIG. 5B, when the finger 502 approaches the touch panel 106, the lines 501 of electric force are blocked. With this, the transient current is reduced.
As shown in FIG. 5C, when a change occurs from the state of FIG. 5A to the state of FIG. 5B, a signal 507 corresponding to a part closest to the finger 502 is significantly lowered. A reduction amount 503 indicates signal intensity. At a part far from the finger, a variation 508 is minute.
FIGS. 6A to 6C are diagrams illustrating a conventional detection method for the touch panel 301. FIG. 6A is a diagram illustrating a state in which a touch operation is not performed, FIG. 6B is a diagram illustrating a state in which a finger 502 has approached the touch panel 106, and FIG. 6C is a graph showing variations of detected signals.
As illustrated in FIG. 6A, one of the X electrode 201 and the Y electrode 202 (in this case, the Y electrode 202) is connected to a voltage source 504 so that a pulse is input thereto from the voltage source 504. A transient current associated with the pulse input from the voltage source 504 is detected by a detection circuit (505, 506) via the other electrode at which capacitive coupling occurs (in this case, the X electrode 201). As illustrated in FIG. 6A, the capacitive coupling forms lines 601 of electric force between the X electrode and the Y electrode. However, compared to the case where the X electrodes 201 and the Y electrodes 202 are present on the same surface as illustrated in FIG. 5B, an amount of the lines 601 of electric force generated outside the display panel is smaller.
As illustrated in FIG. 6B, when the finger 502 approaches the touch panel 301, the lines 601 of electric force are blocked. With this, the transient current is reduced.
However, compared to the case where the X electrodes 201 and the Y electrodes 202 are present on the same surface as illustrated in FIG. 5B, the amount of the lines 601 of electric force generated outside the display panel is smaller, and hence the reduction rate is smaller.
As shown in FIG. 6C, when a change occurs from the state of FIG. 6A to the state of FIG. 6B, a signal 603 corresponding to a part closest to the finger 502 is slightly lowered, but signal intensity is minute. This causes a reduction in detection sensitivity.
FIGS. 7A and 7B are diagrams illustrating visibility (electrode appearance) of the X electrode and the Y electrode in the touch panel 106 and the touch panel 301.
FIG. 7A is a diagram illustrating visibility (electrode appearance) of the X electrode and the Y electrode in the electrode structure of the touch panel 106, and FIG. 7B is a diagram illustrating visibility (electrode appearance) of the X electrode and the Y electrode in the electrode structure of the touch panel 301.
As illustrated in FIG. 7A, in the electrode structure of the touch panel 106, an electrode interval 701 is fine and cannot be easily observed visibly.
As illustrated in FIG. 7B, in the electrode structure of the touch panel 301, an electrode interval 702 is enlarged and can be easily observed visibly.
In the conventional touch panels, for example, when the X electrodes and the Y electrodes are formed on different surfaces and the electrode interval is increased, as in the case of a display device with a built-in touch panel in which a touch panel is built into a display panel, there have been problems in that the detection sensitivity reduces and that the X electrodes and the Y electrodes may be easily observed visibly from the viewer.
When the X electrodes and the Y electrodes are formed on different surfaces and the X electrodes as well as the Y electrodes are densely arranged, the intervals between the X electrodes and between the Y electrodes become fine, and thus the X electrodes and the Y electrodes may not be easily observed visibly from the viewer. In this manner, it is possible to solve the problem in that the X electrodes and the Y electrodes may be easily observed visibly from the viewer.
However, when the X electrodes and the Y electrodes are formed on different surfaces and the X electrodes as well as the Y electrodes are densely arranged, there has been a problem in that it becomes impossible to apply a conventional mutual capacitance detection method (that is, a method of detecting an influence of blocking an electric field between the X electrode and the Y electrode by the finger).
The present invention has been made to solve the above-mentioned problems of the conventional technology, and it is an object of the present invention to provide a touch panel and a display device with a built-in touch panel, which adopt a novel detection method different from a conventional mutual capacitance detection method.